1. Field of the Invention
The present invention relates to a process for preparing pentafluorodichloropropanes. More particularly, the present invention relates to a process for preparing 1,1,1,2,2-pentafluoro-3,3-dichloropropane (hereinafter referred to as "R-225ca") and 1,1,2,2,3-pentafluoro-1,3-dichloropropane (hereinafter referred to as "R-225cb") which are promising substitute compounds for industrially important 1,1,2-trichloro-1,2,2-trifluoroethane and have less influence on global environments.
2. Description of the Related Art
Hitherto, R-225ca and R-225cb have been industrially prepared by reacting tetrafluoroethylene (hereinafter referred to as "TFE") and dichlorofluoromethane (hereinafter referred to as "R-21") in the presence of a catalyst such as anhydrous aluminum chloride at a temperature of from 15 to 100.degree. C. (see J. Amer. Chem. Soc., 71, 979) and Collec. Czechoslov. Chem. Commun., 36, 1867). In addition, R-225ca is prepared by reacting TFE with cesium fluoride in diglyme and then with chloroform (see U.S. Pat. No. 3,381,042).
However, since the above first process reacts the starting materials batchwise in an autoclave or a glass reactor at a temperature of from 15 to 100.degree. C., a selectivity and yield of the desired product is low, for example, the yield is from 46 to 58 % so that this process is industrially uneconomical. In addition, to separate the catalyst from the product after the reaction, the product is collected with a cooled trap under reduced pressure, or the catalyst is treated with dilute hydrochloric acid and then the product is recovered.
In the above second process utilizing cesium fluoride, though the selectivity and the yield of the desired product are good, cesium fluoride which is one of the starting materials is very expensive, so that this process is entirely unsuitable for preparing the desired product industrially.